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James what you are asking is impossible to answer as it depends on a number of parameters like the type of computer you use, the size of your system and the level of accuracy (theory and/or basis set) you want your results to have.
Traditionally for the same system and basis set HF is faster than DFT and DFT is faster than CCSD (the later one coincidentally is an expensive method)
I am sorry I cannot provide a more comprehensive answer but in reality you are constrained by the parameters I have outlined above.
Regardless I hope this helps
AB | SE-444 86 Stenungsund | Sweden
What method are you using (e.g. HF, DFT, CCSD, etc)? This can make a big difference in the run-time. Also what qualifies as a "very long time"?
VCQ Postdoctoral Fellow
Vienna Center for Quantum Science and Technology